The present invention concerns stabilization of polyoxyalkylene polyether polyols and the use of the stabilized polyols in the preparation of polyurethane foam. In particular the invention relates to stabilization of polyols with certain liquid stabilizer compositions and the color or scorch inhibition of flexible and semiflexible polyurethane foams made from the stabilized polyols.
Prior art methods for stabilization of polyoxyalkylene polyether polyols with solid antioxidants or stabilizers and the use of the stabilized polyols in the preparation of polyurethane foams to inhibit scorch are well known.
Conventional solid stabilizers are generally dissolved in the polyol media by heating. To remove any undissolved stabilizer solids, the entire voluminous polyol mass is subjected to a filtration step. Then the polyol precursor can be processed into the final foam product.
U.S. Pat. No. 4,444,676 discloses a method for stabilization of polyoxyalkylene polyether polyols with a solid synergistic stabilizing composition consisting of mixed butylated phenols, p,p'-dialkyldiphenylamine and a phenothiazine compound.
U.S. patent application Ser. No. 07/836,486 now U.S. Pat. No. 5,143,943 teaches a method for reducing scorch of polyurethane foam by incorporating a liquid stabilizer composition consisting of 2,6-di-tert-butyl-4-sec-butylphenol, a reaction product of diisobutylene, styrene and diphenylamine, and a phenothiazine compound. The liquid stabilizer eliminates certain processing disadvantages associated with solid stabilizer systems. The liquid stabilizer compositions are readily soluble in the polyol media at ambient temperatures. Consequently, two steps of the conventional process may be eliminated: dissolution of the stabilizer in the polyol media by heating and removal of undissolved stabilizer solids by filtration. Furthermore, the liquid stabilizer compositions may be added to the polyol by metering or pumping for convenience and safety.
There is a technological need to develop a variety of liquid stabilizer systems for economically sound processing of polyurethane foams for the preparation of various articles useful in the household, packaging, automotive field and industry.
Surprisingly, it has been discovered that tetrakis[methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnimate)]methane and a reaction product of diisobutylene and diphenylamine act synergistically as scorch inhibiors in polyurethane processing. The two component stabilizer composition has the desirable characteristic of being liquid. Furthermore, phenothiazine and certain alkyl derivatives can be incorporated into the stabilizer composition without destroying its liquid character, while synergistically improving the overall scorch inhibiting properties of the stabilizer.